Poly-alpha-olefin compositions containing synergistic stabilizer combination



United Smtes Patent 3,003,996 Patented Oct. TO, 1961 3,003,996 POLY-u-OLEFIN COMPOSITIONS CONTAINING SYNERGISTIC STABILIZER COMBINATION Gordon C. Newland and John W. Tamblyn, Kingsport,

Tenn., assi ors to Eastman Kodak Company, Rochester, N.Y., a corporation of New Jersey No Drawing. Filed May 20, 1959, Ser. No. 814,395 6 Claims. (Cl. 260-453) This invention relates to the stabilization of poly-@- olefin compositions. Preferred embodiments of the invention relate to the stabilization of polyethylene and polypropylene compositions against deterioration resulting from exposure to sunlight or ultraviolet light with novel synergistic stabilizer combinations.

POlY-a-OIGfiHS such as polyethylene, polypropylene and the like are subject to photo-oxidation when exposed to sunlight. This oxidation is characterized in its earlier stages by the breaking of the polymer chain and the formation of carbonyl groups. As the oxidation continues, the polymer cracks and loses tensile strength to the point of mechanical failure. A number of so-called ultraviolet inhibitors are known which inhibit the photo-degradation of many polymers, resins or plastics. However, many effective stabilizers for halogen-containing polymers, for example, such as polyvinyl chloride, polyvinylidene chloride and the like are not efiect-ive stabilizers in polya-olefins as stabilizers in halogen-containing polymers function essentially as hydrogen halide scavengers while stabilizers in halogen-free poly-ot-olefins do not serve this function. Likewise, ultraviolet inhibitors which are eminently suited for such cellulosic esters as cellulose triacetate, cellulose acetate butyrate and the like are not necessarily effective ultraviolet inhibitors for po ly-u-olefins because of the inherently different nature of poly-aolefins. Hence, it is highly unpredictable as to whether a given ultraviolet inhibitor compound will be eifective in poly-u-olefin compositions.

At least as unpredictable is the determination of whether or not a given combination of two or more stabilizer compounds will synergize to produce a stabilizing effect in poly-a-olefins that is greater than the additive elfect of the individual stabilizers. We know of no method whereby a combination of stabilizers can be predicted to be synergistic stabilizers for poly-a-olefin compositions short of actually testing the combination, even though the individual components comprising the combination may be well-known stabilizers for various polymers, resins or plastics, including poly-a-olefin compositions.

Apart from the fact that it is an unexpected scientific discovery when two stabilizers are found that will synergize with each other in poly-a-olefin compositions, there are certain practical advantages that often times accompany the use of such a combination of stabilizers as dis tinguished from the use of a single stabilizer material or compound. For example, one of the stabilizers of the combination might be costly or difiicult to acquire in commercial amounts While the other stabilizer of the combination might be relatively cheap and readily available. In such a situation it would be desirable to be able to substitute the cheaper stabilizer for a portion of the more expensive stabilizer, and still be able to obtain good stabilization through the synergism of the stabilizer combination. Thus, it is highly desirable in the poly-u-olefin art to have available synergistic combinations of two or more stabilizers.

It is an object of this invention to provide new synergistic combinations of stabilizers for poly-a-olefin com positions.

It is another object-of this invention to provide novel polyethylene and polypropylene compositions containing synergistic combinations of compounds that improve the stability of the polyethylene and polypropylene compositions against deterioration resulting from exposure to sunlight or ultraviolet light.

Other objects of the invention will be apparent from the description and claims that follow.

The present invention comprises poly-a-olefin compositions having incorporated therein a stabilizer combination comprising a tris-(dialkylamino)phosph ine oxide and a"2-hydroxy-4,4 dialkoxybenzophenone. This combination imparts to poly-a-olefin compositions a high degree of. stability to deterioration resulting from exposure to ultraviolet light, and which improved stability is substan tially greater than the additive elfect of the individual stabilizers comprising the subject stabilizer combination. Hence, the stabilizer combination of the invention is termed in the art a synergistic combination.

The tris-(dialkylamino)phosphine oxide component of the present combination has the following formula:

wherein R is an alkyl radical, and desirably a lower alkyl radical having 1 to 4 carbon atoms including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tertiary butyl. The preferred tris-(dialkylamino)phosphine is tris-(dimethylaminodphosphine.

The 2-hydroxy-4,4-dialkoxybenzophenone component of the present combination has the following formula:

i no oQ-OR wherein R is an alkyl radical, and desirably a lower alkyl radical having 1 to 4 carbon atoms including methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl and tertiary butyl.

The combination of the subject tris-(dialkylamino)- phosphine oxide and Z-hydroxy-4,4-dialkoxybenzophenone can be used to stabilize a wide variety of poly-a-olefincompositions against deterioration resulting from exposure to ultraviolet light. Any of the normally solid polymers of ot-rnonoolefinic aliphatic hydrocarbons containing 2 to 10 carbon atoms can be stabilized in accordance with the invention. The subject stabilizer combination is preferably used in polyethylene and polypropylene, although such poly-u-olefins as poly 4-methylpentene-1, poly 3-methylbutene1 poly 3,3-dimethyl-butene-l, poly pentene-l, and related homologues are included in the invention. Boththe so-called low density and high density poly-a-olefin compositions can be stabilized in accordance with the invention. Reference is made to 'Fawcett et a1. U.S. Patent .No. 2,153,553 granted April 11, 1939, and to applications Coover U.S. Serial No.

559,536 filed January 17, 1956, now abandoned and inous poly-a-olefin compositions having average molecular weights of at least 15,000 and more usually at least 20,000, as well as the so-called poly-u-olefin waxes having lower molecular weights, usually 3,000-12,000.

The amount of the combination of the subject tris- (dialkylamino)phosphine oxide and 2-hydroxy-4,4'-dialkoxybenzophenone employed in poly-a-olefin compositions in accordance with the invention can be widely varied, the stabilizing amount of this combination usually varying with the particular use to which the poly-a-olefin is to be put. Concentrations of the combination of at least .001% are used, with concentrations of .001% to 10% being generally used, and with concentrations of .005% to being preferably used, the concentration being based on the weight of the poly-u-olefin. The weight ratios of the stabilizers comprising the subject synergistic combination likewise can be varied. We prefer to utilize the combination of the subject stabilizers at weight ratios of tris-(dialkylamino)phosphine oxide to 2-hydroxy-4,4'-dialkoxybenzophenone ranging from A to and preferably A to The stabilizer combinations of the invention can be incorporated or blended into poly-a-olefin compositions by any of the conventional methods used for blending such materials into resins or plastics. Typical of such methods that can be suitably employed include milling on heated rolls, deposition from solvents, and dry-blending. The stabilizers of the invention can be incorporated separately or together into the poly-a-olefin composition.

The stabilizer combinations of the present invention lend to polya-o1efin compositions improved stability, and more specifically, improved stability against deterioration resulting from exposure to sunlight or ultraviolet light. Thus, poly-a-olefins stabilized in accordance with the invention have an extended life expectancy and can be used more effectively than unstabilized poly-a olefins for a wide diversity of uses, including outdoor uses requiring prolonged exposure to the elements. Poly-aolefins stabilized in accordance with the invention can be cast, extruded, rolled or molded into sheets, rods, tubes, piping, filaments and other shaped articles. The present compositions can be used for coating paper, wire, metal foil, glass fiber fabrics, synthetic and natural textiles and other such materials. Likewise, small amounts of other additives such as other polymers, resins or plastics, as well as other stabilizers or inhibitors, that are commonly added to POlY-Ot-OlBfiIlS for specific uses are not deleterious to the effectiveness of the present synergistic combination.

The invention is illustrated by the following examples of preferred embodiments thereof.

Example 1 Polypropylene samples containing 1% by weight of 2-hydroxy-4,4'-dimethoxybenzophenone plus 2% by weight of tris-(dimethylamino)phosphine oxide, as well as these two stabilizers individually at a level of 3% by weight and a control containing no stabilizer additive, were subjected to artificial weathering. The additives were incorporated into polypropylene having an average molecular weight of about 126,000 and a density of .917. The polypropylene compositions were injection molded into A inch thick samples. The prepared samples were exposed in an Atlas Twin-Arc Weather- Ometer as described in Anal. Chem., 25, 460 (1953) that was modified by the addition of 10 Westinghouse 20 watt sunlamps. Exposure damage to the samples was assessed by physical appearance of the exposed samples and by determining the percent of original elongation retained after 700 hours of exposure to the artificial weathering. The elongation measurements were determined on 2.5 x .5 inch test strips with an Instron tensile tester at a rate of stretch of 2,000% per minute. The test samples were conditioned one week at 73 F. at a relative humidity of 50%. The results of the tests are summarized by the data set out in Table A below.

TABLE A Percent Original Appearance of Additive Elongation Surface Alter 700 Left After Hours Exposure 700 Hours Exposure (1) None--. 7 Rough, crumbly. (2) 3% Trls-(dimethylamino) phos- 29 Powdery.

phine oxide. (3) 3% 2-Hydroxy-4,4-dimethoxy- 59 Slightly powdery.

benzophenoue. (4) 2% Tris-(dimethylamino) phos- 103 Smooth, tough.

phine oxide+1% 2-Hydroxy-4,4-dimethoxy-benzophenonc.

As can be seen from the data set out in Table A, tris- (dimethylamino)phosphine oxide and 2-hydroxy-4,4-dimethoxybenzophenone cooperate to lend to polypropylene a resistance to ultraviolet degradation that is greater than that resulting from these two additives individually.

Example 2 A 2% by weight portion of tris-(dimethylamino)phosphine oxide in combination with a 1% by weight portion of 2-hydroxy-4,4-dimethoxybenzophenone incorporated into polyethylene having an average molecular weight of about 30,000 and a density of .918, when prepared in test samples and exposed to artificial weathering as described in Example 1, show a synergistic efifect in stabilizing the polyethylene against deterioration resulting from the exposure.

Example 3 Tris-(dirnethylamino)phosphine oxide and Z-hydroxy- 4,4-dimethoxybenzophenone can be employed in combination with other stabilizer materials to improve poly-aolefins against deterioration resulting from exposure to ultraviolet light. Several of such stabilizer combinations were incorporated into polypropylene, exposed and tested as described in Example 1. The results of the tests are summarized by the data set out in Table B below which is a continuation of Table A.

phine oxide-{4% 2-Hydroxy-4,4-dimethoxybenzophenone+1% 4,4-Butylldene bls-(6-tert.-butyl-m-eresol) The present invention thus provides novel poly-u-olefin compositions having improved stability against deterioration resulting from exposure to ultraviolet light, and particularly it provides novel and useful synergistic stabilizer combinations for poly-ot-olefin compositions.

Although the invention has been described in detail with reference to preferred embodiments thereof, it will be understood that variations and modifications can be effected within the spirit and scope of the invention as described hereinabove and as defined by the appended claims.

We claim:

1. A solid poly-m-olefin composition comprismg a p y-e-vlefin selected from the group consisting of polyand a 2-hydroxy-4,4'-dialkoxybenzophenone having the formula wherein the R substituents in the said formulas are lower alkyl radicals having 1 to 4 carbon atoms, the weight ratio of said tris-(dialkylamino)phosphine' oxide to said 2-hydroxy-4,4'-dialkoxybenzophenone being in the range of 1/30 to 30/1.

2. A solid poly-a-olefin composition comprising polyethylene containing .005% to 5% by weight based on said polyethylene of a stabilizer combination comprising tris-(dimethylamino)phosphine oxide and 2-hydroxy-4,4s dimethoxybenzophenone, the Weight ratio of said tris- (dimethylamino)phosphine oxide to said 2-hydroxy-4,4'- dimethoxybenzophenone being in the range of 1/10 to 1.

3. A solid poly-a-olefin composition comprising polypropylene containing .005 to 5% by weight based on said polypropylene of a stabilizer combination comprising tris-(dimethylamino)phosphine oxide and 2-hydroxy- 4,4'-dimethoxybcnzophenone, the weight ratio of said tris-(dimethylamino)phosphine oxide to said 2rhydroxy- 4,4-dimethoxybenzophenone being in the range of 1/10 to 10/ 1.

4. A solid poly-a-olefin composition comprising polyethylene having an average molecular Weight of at least 15,000 containing about 2% by weight based on said polyethylene of tris-(dimethylamino)phosphine oxide and about 1% by weight based on said polyethylene of 2-hydroxy-4,4'-dimethoxybenzophenone.

5.A solid poly-a-olefin composition comprising polypropylene having an average molecular weight of at least 15,000 containing about 2% by weight based on said polypropylene of tris-(dimethylamino)phosphine oxide and about 1% by weight based on said polypropylene of 2-hydroxy-4,4'-dimethoxybenzophenone.

6. A solid poly-a-olefin composition comprising a poly-u-olefin selected from the group consisting of polyethylene and polypropylene containing .001% to 10% by weight based on said poly-a-olefin of a stabilizer combination comprising tris-(dimethylamino) phosphine oxide and 2-hydroxy-4,4-dimethoxybenzophenone, the weight ratio of said tris-(dimethylamino) phosphine oxide to said 2-hydroxy-4,4-dimethoxybenzophenone being in the range of l/ to 30/1.

References Cited in the file of this patent UNITED STATES PATENTS 2,587,549 Trementozzi Feb. 26, 1952 2,682,559 Stanley et a1. June 29, 1954 2,877,204 Duhnkrack Mar. 10, 1959 

1. A SOLID POLY-A-OLEFIN COMPOSITION COMPRISING A POLY-A-OLEFIN SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE AND POLYPROPYLENE CONTAINING .001% TO 10% BY WEIGHT BASED ON SAID POLY-A-OLEFIN OF A STABLIZER COMBINATION COMPRISING A TRIS-(DIALKYLAMINO)PHOSPHINE OXIDE HAVING THE FORMULA 